1. Field of the Invention
This invention relates to solenoids and has particular reference to solenoids of the general type having an armature of magnetic material which is slideable endwise within an electromagnetic coil and which is drawn within the coil upon energization of the latter.
2. Description of the Prior Art
Solenoids of the above type exert an actuating force along the length of travel of the armature. Generally, in order to provide maximum efficiency, a stationary core or other element of magnetic material is provided at the end of the coil opposite the armature in order to concentrate the magnetic flux in the path of the armature and across the gap between the armature and the core element. This results in the armature exerting a force which increases as it approaches the end of its travel, i.e., as it approaches the core element. Such increase in force generally develops at substantially an exponential rate and, without a shock absorber of some kind, the armature tends to slam into the core or other stop element, creating a loud noise and jarring effect. Such noise etc., is undesirable in certain applications, such as in calculating and business machines intended to be used in offices or other places where noise is highly objectionable.
Heretofore, the above problem has usually been solved by providing an elastomeric bumper which is attached to some stationary element, such as the solenoid frame, and is located in the path of the armature or other element operated thereby. In order to effectively bring the armature and any train of elements connected thereto to a halt without creating the above noted noise or jarring effect, the bumper must normally be made relatively large and the material thereof must be made soft enough to gradually absorb the shock over a relatively long distance. Additionally, adjustment provisions must normally be provided in cases where it is desirable to have the armature come to rest at a precise location.
It is known that if the bumper is made with a blunt or flat engaging surface, the initial impact of the armature may still tend to produce a jarring effect unless the bumper is made of extremely soft material. This effect is decreased by forming the bumper with a semi-spherical or conical engaging end so that the initial impact is less and the resistance to deformation of the bumper gradually increases as the armature approaches the end of its travel. However, since the bumper must be supported at one end, only the opposite end can be so formed to provide such gradually increased resistance to the movement of the armature.